1. Field of the Invention
The application relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of enhancing uplink power control in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as to user equipments (UEs).
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system, considering relaying for cost-effective throughput enhancement and coverage extension. The LTE-A system includes all of the features of the LTE system and several new ones, the most important of which are: carrier aggregation, enhanced multi-antenna support and relaying. The LTE system provides extensive support for deployment in spectrum allocations of various characteristics, with transmission bandwidths ranging from 1.4 MHz up to 20 MHz. In the LTE-A system, the transmission bandwidth can be further extended with carrier aggregation wherein multiple component carriers are aggregated and jointly used for transmission to/from a signal UE. In general, up to five component carriers can be aggregated, allowing for transmission bandwidth up to 100 MHz.
Power control is about setting transmit power levels, typically with the aim of improving system capacity, coverage, and user quality (data rate or voice quality) and reducing power consumption. To reach these objectives, power-control mechanisms typically attempt to maximize the received power of desired signals while limiting interference.
The LTE uplink is orthogonal, which is, at least in the ideal case, no interference between users in the same cell. The amount of interference to neighbor cells depends, among other things, on the position of the UE-more specifically, on the path gain from the terminal to these cells. In general, the closer the UE is to a neighboring cell the stronger the interference to that cell.
For uplink (UL) power control, it is necessary to provide UE with a proper UL transmission power (e.g. to save power) and to restrict UL interference. In LTE system, both downlink (DL) and UL power control are defined. Power headroom report (PHR) is triggered according to 3GPP TS 36.321.
To assist the network scheduler, a media access control (MAC) layer of UE performs and reports channel measurement. The PHR informs the network of the difference between the UE's current transmit power and its maximum transmit power.
In LTE-A system (e.g. Rel-10), it's been agreed that simultaneously PUCCH and PUSCH transmission. Consequently, eNB should take into account PUCCH transmission power contributing to the UE current transmission power so as to assist eNB to schedule PUSCH. The composite PUCCH/PUSCH PHR doesn't provide enough information on the PUCCH and PUSCH transmission power level. In addition, accumulative PUCCH and PUSCH power control error could happen (e.g. miss detection or detection error).
It's agreed in LTE-A system (e.g. Rel-10) to have one UE specific UL CC configured for PUCCH. Consequently, PUCCH PHR should only be reported on the configured UL CC since PHR is CC specific. However, there should be another alternative since eNB knows on which UL CC PUCCH is allowed to be transmitted.
The eNB should determine PUSCH grant/Modulation and coding scheme (MCS) according to its knowledge on when PUCCH has occurred or is going to occur. However, miss detection/detection error (e.g. PUCCH content) and Transmission Power Control (TPC) command errors could happen.